import { Inject, Injectable } from '@nestjs/common';
import { BackgroundJobRecord, ClaimJobInput, JOBS_PRISMA } from './jobs.types';

const DEFAULT_LEASE_MS = 60_000;

@Injectable()
export class JobLockService {
  constructor(@Inject(JOBS_PRISMA) private readonly prisma: any) {}

  async claimNext(input: ClaimJobInput): Promise<BackgroundJobRecord | null> {
    const now = input.now ?? new Date();
    const leaseMs = input.leaseMs ?? DEFAULT_LEASE_MS;
    const types = input.types?.map((type) => type.trim()).filter(Boolean) ?? [];

    return (this.prisma as any).$transaction(async (tx: any) => {
      const params: unknown[] = [now];
      const typeCondition = buildTypeCondition(types, params);
      const rows = await tx.$queryRawUnsafe(
        `
SELECT id
FROM background_jobs
WHERE (
    (status = 'queued' AND available_at <= $1)
    OR (status = 'running' AND locked_until IS NOT NULL AND locked_until < $1)
  )
  ${typeCondition}
ORDER BY available_at ASC, created_at ASC
LIMIT 1
FOR UPDATE SKIP LOCKED
`,
        ...params,
      );
      const id = rows[0]?.id;
      if (!id) return null;

      return tx.backgroundJob.update({
        where: { id },
        data: {
          status: 'running',
          lockedBy: input.workerId,
          lockedUntil: new Date(now.getTime() + leaseMs),
          attempts: { increment: 1 },
          lastError: null,
        },
      });
    });
  }
}

function buildTypeCondition(types: string[], params: unknown[]): string {
  if (types.length === 0) return '';
  const placeholders = types.map((type) => {
    params.push(type);
    return `$${params.length}`;
  });
  return `AND type IN (${placeholders.join(', ')})`;
}